Contact printing emulsion and method of making



Aug. 23, 1955 J. M. LUPO, JR 2,716,060

CONTACT PRINTING EMULSION AND METHOD OF MAKING Filed July 7, 1950 IN V EN TOR.

United States Patent Gfiice 2,716,060 Patented Aug. 23, 1955 CONTACT PRINTING EMULSION AND METHOD OF MAKING John 1V1. Lupo, Jr., Brooklyn, N. Y., assignor to Direct Reproduction Corporation, a corporation of New York Application July 7, 1950, Serial No. 172,401

2 Claims. (Cl. 957) This invention relates to a contact printing emulsion and the method of making it.

The art of contact printing, in printing or recording engineering drawings and the like, has been known for fifteen years or more and is now in extensive use. In this art it is important, particularly in drawings which show dimensions, that the sheet on which the printing is made be one of dimensional stability, that is, free from changes in dimensions to an objectionable extent with changes in humidity or other conditions to which the sheet may be subjected in use. This means that the preferred materials for the printing are such products as glass and vinyl or other plastics.

A difliculty has arisen, however, in the contact printing on such materials as the plastics and glass; the composition serving as the ink does not undergo absorption or adhere sufficiently to the surface on which the printing is made.

The present invention provides a method of making a contact printing emulsion and also a new emulsion that is absorbed and held satisfactorily on glass, vinyl plastics, or the like and that gives a sharply defined, intense print.

Briefly stated, my invention comprises a contact printing emulsion including a light sensitive base, pigmentary material of hydrophilic and also lipophilic properties, an emulsifier for the pigmentary material, an alkali establishing the pH at a figure above 7, and water, the light sensitive base being dissolved or dispersed as a colloid in the Water and the pigmentary material being suspended in the water. Finally the entire mixture is subjected to a special type of milling operation which reduces the particle size of the solids and gives uniform dispersion of the various ingredients.

With the emulsion of the kind described, I am able to make sharply defined prints. In these, the printing emulsion adheres firmly to the sheet upon which the printing is made and remains adhered after repeated flexing of the base sheet, in case the sheet used is one that is flexible.

Once these eiiects are observed, various theories may be advanced to explain the effects. I consider that the lack of absorption and adherence of conventional contact printing emulsions on vinylite plastics and the like has been due to excessive hydrophilic property and attendant lack of adequate lipophilic property in the contact emulsion, particularly in the pigmentary material. I have solved this problem by the use of pigmentary material that is hydrophilic, so that it may dispersed in aqueous solutions and, on the other hand, also lipophilic, so that it wets and adheres to the vinyl plastics, glass, and like surfaces that are impenetrable to hydrophilic materials.

As to the method of the invention, this comprises the very fine milling of pigmentary material, as described herein, to a state of subdivision which is much finer than that in which even fine pigments are ordinarily supplied in commerce.

I accomplish this fine milling by special means which will be described in connection with the attached drawing to which reference is made.

The single figure of the drawing is a side elevation of a mill used in reducing pigmentary material to the necessary fineness. The view is partly in section and parts not shown are conventional.

In this figure, there are shown a hopper 10 for a supply of the aqueous suspension of material such as lamp black that is to be milled, a screw conveyor 12 feeding this suspension within the case 14 of the mill, and a motor driven rotor with bars 16 for milling the said material. The drive for this rotor is conventional and not shown.

Disposed within the case is the milling plate 18 with generally saw-toothed interior, against which the rotor, with the hammers 20 hurl the suspension with great force.

At the bottom of the mill, is the outlet plate 22 provided with the slots 24 shown therein. These slope in the direction of rotation of the charge under the influence of the hammers 23. The width of these slots in a satisfactory constniction is about 0.01 inch. Because of the slope in the direction of rotation of the mass undergoing milling, the particles which obtain access to and pass through the slots must be something less than 0.01 inch in shortest dimension.

The mill has an outlet spout 28. Through this the milled suspension or paste, that has passed through the plate 22, moves to a convenient receptacle as indicated at 29.

The milling step will be in part obvious from the description of the apparatus that has been given. The selected pigmentary material is mixed into a suspending medium such as a dispersion of gum arabic in water. The resulting mixture is then delivered to the grinding chamber of the mill, as by the screw conveyor feed. The hammers are then rotated at very high speed, as, for instance, 14,500 R. P. M., this being for a mill in which the length I of the bars from the points of support is about 4 inches.

Under this high speed rotation, the suspension of the pigment in the gum arabic solution is thrown to the outside of the mill and is driven with great force against the milling plate with the saw tooth edge and eventually over the entrances to the outlets through the screen or plate at the bottom of the mill. This screen is in the form of an arc of rigid metal having cross cuts of very small width such as that stated.

In place of the gum arabic solution used for this illustration of the method of milling there may be used other media for suspending the material to be ground. Thus there may be used any one of the colloidal solutions disclosed below, for use in the light sensitive base for the contact printing emulsions.

As to the materials which are employed in my emulsion, I require, first of all, a light sensitive base. This is a base which, when applied as a film over a surface such as glass or a plastic, becomes changed by exposure to light in such way that the exposed base is not removed by the usual developing and washing operations.

The light sensitive base includes a water dispersible colloid and a water soluble dichromate. Under the infiuence of incident light the mixed dichromate and colloid become changed to less soluble form; at the positions of' exposure to the light, the base, consisting of the colloid and dichromate, forms the outline of the printing after the usual developing and washing operation.

As the colloid in the light sensitive base, I prefer to use gum arabic. In place of the gum arabic, I may use glue,

gum tragacanth, gelatine, and various derivatives of cellulose that are dispersible as colloids in water, all of which are thickeners for water. cellulose, hydroxymethyl cellulose, and methyl celluose.

As the dichromate, I use preferaby ammonium dichromate. Although there may be used other soluble dichromates, such as the potassium or sodium dichromate, there is no advantage in the replacement and the other dichro- Examples are carboxymethyl mates are not nearly as fast in operation as the ammonium' dichromate. This means that they require longer exposure to light to give the same intensity of printing after development.

As'pigment, I have found just one type of black material which gives the desired adherence and absorption to the non-hydrophilic surfaces such as those of vinyl plastics and glass. This is lamp black characterized by having both hydrophilic and lipophilic properties.

The suitability of any commercial lamp black for my purpose may be tested in simple manner, as follows: Shake the lamp blackwith a large proportion of water in a testtube. If the lamp black settles to the bottom of the test tube after shaking, this means that the lamp black is readily wettable with water and, therefore, hydrophilic to the exclusion of lipophilic property to such an extent as to be unsatisfactory for my purpose. This simple test may be confirmed byanother test. In this other test, the lamp black is shaken again with a large proportion of water in a test tube. If the lamp black on subsequent standing rises to the surface of the water, this shows that the lamp black is non-wettable by water, i. e., has not been wetted with -the water to the extent of replacing the air in the powder so that the powder may sink. It shows, also, that such lamp black is sufiiciently lipophilic for my purpose. The lamp black'which resists wetting by water and which, therefore, rises in the test described is properly referred to as both hydrophilic and lipophilic. A representative lamp black that is both hydrophilic and lipophilic is one which is known as Monsanto 2. This lamp black, in the standard oil absorption test by the spatula method, shows an absorption of more than its weight of oil, as, for instance, 109%. This particular lamp black has a carbon c'ontent'above 99% and ordinarily 99.4%.

The emulsifier in my composition is a water soluble wetting and emulsifying agent that is chemically inert to the other ingredients of the composition. For best results,

it should be at least moderately active as an humectant, unless-an added humectant is to be used, this in order to improve the permanent flexibility of the contact printing composition in equilibrium with atmospheric humidity on the printed sheet. Examples of emulsifiers that meet these requirements and that are satisfactory for use are glycerine which is the preferred material, triethanolamine, and sorbitol.

The alkali added to increase the sensitivity of the light sensitive base is preferably ammonium hydroxide. There isno advantagein using potassium or sodium hydroxide although those may be used under some circumstances, particularly inrcase the dichromate present in the base is the potassium or sodium salt.

Water is usedas the dispersing and suspending medium.

The proportions of the various classes of ingredients of my emulsion are stated as parts for 100 parts of water, all proportions here and elsewere herein being expressed as parts by weight.

Parts for 100 Parts of'Water Glass and Illustrative Ingredient For Best 7 Commercial Permissible Results Colloid (gum arabic) on dry basis 25 -35. Dlchromate (ammonium diehmmate) 15 to saturation proportion. Plgmentary material (special lamp 8.5 12.

black Emulsifier (glycerine) 3 l. 2 4. Alkali (ammonium hydroxide) to es- 8-8.4 7. 5-10.

tablish pH at. Waten; 100 100. Density of Emulsion 14 Be Iii-15 Be.

As to certain proportions more specifically, the dichro mate is required in such amount that, after the light exposure, there is precipitation of insoluble material. The

. proportion of ammonium dichromate that gives the best 4 results commercially is approximately 15 to 30 parts, as compared to maximum or saturation proportion of 34 parts for of water.

As to the pigment, it is essential that the proportion used give the desired tinting or intensity of printing in the final use. It is essential also that the proportion used be insufficient to obscure the light sensitive base from exposure to the printing light. With my special pigment, I find that the proportions given in the table make possible both the access of the light to the sensitive base and also the desired intensity of printing.

The invention will be further illustrated by description in connection with the following specific examples of it.

Example 1 of glycerine and of ammonium hydroxide in amount to establish the pH at 8.2.

The final mixture of these proportions is then passed through a micropulverizer, of kind shown in the drawing and operated as described above and repassed, for a total of three or more times. livered by the screw conveyor to the chamber of the mill, is rotated by the rotor and hammers and hurled at very high velocity against the roughened imilling surface of part 18. The milling operation is continued, for a given 7 particle, until that particle becomes so small as to pass through one of the outlet openings in plate 22. The final product is then pressure-filtered through cloth and is ready for use in contact emulsion printing by steps which,

from this point forward, are conventional.

Example 2 The procedure of Example 1 is followed except that there is substituted for the gum arabic an equal weightof any one of the other colloid thickeners which are given above as alternatives for the gum arabic.

Example 3 The procedure of Example 1 is' followed except that the glycerine is substituted on an equal weight basis by triethanolamine or sorbitol.

Example 4 This example illustrates the use of the method of the present invention in milling other pigments than the special lamp black. The procedure and the proportions of Example 1 are followed except that the special lamp black is substituted on an equal tinting basis by any one of the following pigmentary materials:

Toluidine red toner Phthalocyanine blue Hansa yellow (Ferrox yellow) The proportions of these pigments which are required, to give the intensity of color desired in the contact emulsion, are determined by a simple experiment or in accordance with manufacturers directions.

materials used.

The method of milling the pigments as described is satisfactory for a wide range of pigmentary material but it is an important feature of my invention that all of the ingredients that are to be included in the finished emulsion are combined before the milling step is taken in order that there maybe a proper relationship of the various ingredi ents employed. This means that the. dichromate must be present during the milling operation and it is well known Here the suspension, de-

The numerical 1 values will not be the same for each of the pigmentary that dichromate is heat sensitive. The particular type of milling which I recommend, which involves suspending the pigment in the various liquid ingredients and then throwing it at extremely high velocity by the hammermill type of mechanism against a grinding surface, does not develop heat in the same way as where friction plates are employed.

The contact emulsions, made with the special lamp black that is both hydrophilic and lipophilic, give the desired absorption and adherence on water repellent sheets such as those of cellulose acetate, styrene, and polyethylene in addition to glass and the various, usual types of vinyl resins, including the polyvinyl chloride resins and vinyl chloride and acetate copolymers. Best results are obtained when the sheets on which the printing is to be made are roughened, as by pressing of the plastic sheet, at the time of formation, against a roughened surface giving a mechanical grain or mat effect. In the case of a sheet of glass the printing is more satisfactory when the glass has been roughened, as by sand blasting or other usual commercial method.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

What I claim is:

l. The method of preparing a contact printing emulsion adapted to be retained on plastic and glass surfaces which comprises mixing approximately 100 parts by weight of water with approximately 6 to 12 parts by weight of a pigment selected from the group consisting of toluidine red toner, phthalocyanine blue, hansa yellow, and a lamp black pigment having at least 99% by weight of carbon which is capable of adsorbing more than its of approximately 2 to 4 parts by weight of a humectant and emulsifying agent selected from the group consisting of glycerine, triethanolamine and sorbitol and adding ammonium hydroxide in an amount to establish a pH of approximately 7.5 to 10.0 and then delivering the entire mixture into the chamber of a mill, rotating the mixture in such chamber to hurl it at high velocity and by centrifugal force against a rough milling surface and continuing the milling operation for a given particle of solid until the particle is reduced in size to pass through an opening of predetermined size in the outlet of the mill to emulsify and uniformly disperse the solid pigment particles and ammonium dichromate throughout the resulting emulsion whereby the emulsion upon exposure to light will adhere to a flexible sheet such as a vinyl plastic sheet in a substantially continuous film even after repeated flexing of the sheet.

2. The contact printing emulsion produced by the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 68,248 Smith Aug. 27, 1867 114,693 Lewis May 9, 1871 120,136 Wenderoth Oct. 17, 1871 1,511,987 Thomas Oct. 14, 1924 1,704,356 Bakers et al. Mar. 5, 1929 2,061,230 Frankenburger et al. Nov. 17, 1936 2,271,234 Staud et al. Jan. 27, 1942 2,327,828 Simmons Aug. 24, 1943 FOREIGN PATENTS 27,686 Great Britain July 22, 1909 573,771 Great Britain Dec. 5, 1945 OTHER REFERENCES Mattiello, Protective and Decorative Coatings, vol. II, pages 489-493. Pub. by Wiley & Sons, Inc., New York (1942).

Lietze, Modern Heliographic Processes. Pub. by D. Van Nostrand Company, New York (1888), page 111. 

1. THE METHOD OF PREPARING A CONTACT PRINTING EMULSION ADAPTED TO BE RETAINED ON PLASTIC AND GLASS SURFACES WHICH COMPRISES MIXING APPROXIMATELY 100 PARTS BY WEIGHT OF WATER WITH APPROXIMATELY 6 TO 12 PARTS BY WEIGHT OF A PIGMENT SELECTED FROM THE GROUP CONSISTING OF TOLUIDINE RED TONER, PHTHALOCYANINE BLUE, HANSA YELLOW, AND A LAMP BLACK PIGMENT HAVING AT LEAST 99% BY WEIGHT OF CARBON WHICH IS CAPABLE OF ADSORBING MORE THAN ITS WEIGHT OF OIL, ADDING APPROXIMATELY 15 TO 35 PARTS BY WEIGHT OF A WATER DISPERSIBLE COLLOID SELECTED FROM THE GROUP CONSISTING OF GUM ARABIC, GUM TRAGACANTH, GELATINE, CARBOXYMETHYLCELLULOSE, HYDROXYMETHYL CELLULOSE AND METHYLCELLULOSE AND APPROXIMATELY 15 TO 30 PARTS BY WEIGHT OF AMMONIUM DISCHROMATE FOLLOWED BY THE ADDITION OF APPROXIMATELY 2 TO 4 PARTS BY WEIGHT OF A HUMECTANT AND EMULSIFYING AGENT SELECTED FROM THE GROUP CONSISTING OF GLYCERINE, TRIETHANOLAMINE AND SORBITOL AND ADDING AMMONIUM HYDROXIDE IN AN AMOUNT TO ESTABLISH A PH OF APPROXIMATELY 7.5 TO 10.0 AND THEN DELIVERING THE ENTIRE MIXTURE INTO THE CHAMBER OF A MILL, ROTATING THE MIXTURE IN SUCH CHAMBER TO HURL IT AT HIGH VELOCITY AND BY CENTRIFUGAL FORCE AGAINST A ROUGH MILLING SURFACE AND CONTINUING THE MILLING OPERATION FOR A GIVEN PARTICLE OF SOLID UNTIL THE PARTICLE IS REDUCED IN SIZE TO PASS THROUGH AN OPENING OF PREDETERMINED SIZE IN THE OUTLET OF THE MILL TO EMULSIFY AND UNIFORMLY DISPERSE THE SOLID PIGMENT PARTICLES AND AMMONIUM DICHROMATE THROUGHOUT THE RESULTING EMULSION WHEREBY THE EMULSION UPON EXPOSURE TO LIGHT WILL ADHERE TO A FLEXIBLE SHEET SUCH AS A VINYL PLASTIC SHEET IN A SUBSTANTIALLY CONTINUOUS FILM EVEN AFTER REPEATED FLEXING OF THE SHEET. 